Prepreg, fiber-reinforced composite material, and resin composition containing particles

ABSTRACT

A prepreg  10  comprises: a reinforcing fiber layer  3  including reinforcing fibers  1  and a resin composition  2  with which the space between fibers of the reinforcing fibers  1  is impregnated and which contains (A) a benzoxazine resin, (B) an epoxy resin, and (C) a curing agent having 2 or more phenolic hydroxy groups in a molecule; and a surface layer  6   a  or  6   b  provided on at least one surface of the reinforcing fiber layer  3  and containing (A) a benzoxazine resin, (B) an epoxy resin, (C) a curing agent having 2 or more phenolic hydroxy groups in a molecule, and (D) polyamide resin particles  4  having an average particle size of 5 to 50 μm, wherein the polyamide resin particles  4  include a particle made of a polyamide  11.

TECHNICAL FIELD

The present invention relates to a prepreg, a fiber-reinforced compositematerial, and a resin composition containing particles used for thepreparation of them. The present invention particularly relates to afiber-reinforced composite material for aircraft uses, vessel uses,automobile uses, sports uses, and other general industrial uses and aprepreg used to obtain the composite material.

BACKGROUND ART

Fiber-reinforced composite materials made of various fibers and matrixresins are widely used for aircraft, vessels, automobiles, sportsequipment, other general industrial uses, etc. because of theirexcellent mechanical properties. In recent years, with actual uses ofthem, the range of use of fiber-reinforced composite materials has beenbecoming wider and wider.

As such fiber-reinforced composite materials, ones using a benzoxazineresin are proposed in, for example, Patent Literatures 1 and 2. Thebenzoxazine resin has excellent moisture resistance and heat resistance,but has the problem of being inferior in toughness; and measures inwhich epoxy resins, various resin fine particles, etc. are blended tomake up for the disadvantage are taken.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open No.2007-16121

Patent Literature 2: Japanese Patent Application Laid-Open No.2010-13636

SUMMARY OF INVENTION Technical Problem

For fiber-reinforced composite materials for aircraft uses, furtherweight reduction is desired. To reduce the weight of the material, it isnecessary to achieve, in particular, a compressive strength after impact1.0 (hereinafter, abbreviated as a CM) and a flexural modulus out of themechanical characteristics needed for aircraft uses at high level at thesame time, and it is also necessary for the glass transition temperatureof the resin material used to be kept high in order to maintain hightemperature characteristics. However, it cannot necessarily be said thatthese can be achieved at high level at the same time in the examplesspecifically described in Patent Literatures above.

An object of the present invention is to provide a prepreg that makes itpossible to obtain a fiber-reinforced composite material that, whileusing a benzoxazine resin having excellent moisture resistance and heatresistance, can achieve an excellent CAI and flexural modulus at highlevel at the same time and can also keep the glass transitiontemperature of the resin material high, a resin composition containingparticles for obtaining the prepreg, and a fiber-reinforced compositematerial.

Solution to Problem

To solve the problem mentioned above, the present invention provides aprepreg comprising: a reinforcing fiber layer including reinforcingfibers and a resin composition with which the space between fibers ofthe reinforcing fibers is impregnated and which contains (A) abenzoxazine resin, (B) an epoxy resin, and (C) a curing agent having 2or more phenolic hydroxy groups in a molecule; and a surface layerprovided on at least one surface of the reinforcing fiber layer andcontaining (A) a benzoxazine resin, (B) an epoxy resin, (C) a curingagent having 2 or more phenolic hydroxy groups in a molecule, and (D)polyamide resin particles having an average particle size of 5 to 50 μm,wherein the polyamide resin particles include a particle made of apolyamide 11.

By the prepreg of the present invention being stacked plurally andheated under increased pressure, a fiber-reinforced composite materialthat, while using a benzoxazine resin having excellent moistureresistance and heat resistance, can achieve an excellent CAI andflexural modulus at high level at the same time and can also keep theglass transition temperature of the resin material high can be obtained.

The present inventors presume the reason why the CAI and the flexuralmodulus can be improved by the prepreg mentioned above as follows. Adecrease in the melting temperature of the polyamide resin particlesoccurs due to the presence of the compound having phenolic hydroxygroups that is the curing agent of (A) the benzoxazine resin. Here, ifthe melting temperature of the polyamide resin particles is too low,during the curing of the thermosetting resin in preparing afiber-reinforced composite material using the prepreg, the polyamideresin particles are likely to melt and the melted polyamide resinparticles are likely to enter the reinforcing fiber layer; but it ispresumed that, by using the specific polyamide resin particles mentionedabove, a state where it is difficult for the polyamide resin particlesto flow can be created and consequently the effects of improving the CAIand the flexural modulus have been able to be obtained sufficiently. Inaddition, it is presumed that also the fact that the polyamide resinparticles mentioned above melt a little during the preparation of afiber-reinforced composite material has contributed to the improvementof the CAI and the flexural modulus.

It is preferable that the surface layer mentioned above contain 65 to 78parts by mass of the (A) component mentioned above, 22 to 35 parts bymass of the (B) component mentioned above, 5 to 20 parts by mass of the(C) component mentioned above, and 15 to 45 parts by mass of the (D)component mentioned above when it is assumed that the total amount ofthe (A) component mentioned above and the (B) component mentioned aboveis 100 parts by mass.

The present invention also provides a fiber-reinforced compositematerial obtained by stacking the prepreg of the present inventionmentioned above plurally and performing heating under increasedpressure.

By being obtained from the prepreg according to the present invention,the fiber-reinforced composite material of the present invention hasexcellent moisture resistance and heat resistance and can achieve anexcellent CAI and flexural modulus at high level at the same time. Bythe fiber-reinforced composite material of the present invention, theweight of the material can be reduced through the excellent physicalproperties mentioned above.

The present invention also provides a resin composition containingparticles comprising (A) a benzoxazine resin, (13) an epoxy resin, (C) acuring agent having 2 or more phenolic hydroxy groups in a molecule, and(D) polyamide resin particles having an average particle size of 5 to 50μm, wherein the polyamide resin particles include a particle made of apolyamide 11.

By the resin composition containing particles of the present invention,the surface layer of the prepreg according to the present inventiondescribed above can be fabricated.

Advantageous Effects of Invention

According to the present invention, a prepreg that makes it possible toobtain a fiber-reinforced composite material that, while using abenzoxazine resin having excellent moisture resistance and heatresistance, can achieve an excellent CM and flexural modulus at highlevel at the same time and can also keep the glass transitiontemperature of the resin material high, a resin composition containingparticles for obtaining the prepreg, and a fiber-reinforced compositematerial can be provided.

The fiber-reinforced composite material of the present invention can besuitably used for aircraft uses, vessel uses, automobile uses, sportsuses, and other general industrial uses, and is useful particularly foraircraft uses.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is schematic cross-sectional views for describing prepregsaccording to the present invention.

FIG. 2 is schematic cross-sectional views for describing a productionmethod for a prepreg according to the present invention.

FIG. 3 is schematic cross-sectional views for describing a productionmethod for a prepreg according to the present invention.

FIG. 4 is a schematic cross-sectional view for describing afiber-reinforced composite material according to the present invention.

FIG. 5 is a DSC chart of PA 6/12 (80/20).

FIG. 6 is a DSC chart of a second resin composition of Example 3.

DESCRIPTION OF EMBODIMENTS

The present invention will now be described in detail.

FIG. 1 is schematic cross-sectional views for describing a prepregaccording to the present invention. A prepreg 10 shown in (a) of FIG. 1comprises: a reinforcing fiber layer 3 including reinforcing fibers 1and a resin composition 2 with which the space between fibers of thereinforcing fibers 1 is impregnated; and a surface layer 6 a provided ona surface of the reinforcing fiber layer 3 and containing polyamideresin particles 4 and a resin composition 5. In the surface layer 6 a ofthe prepreg 10, the polyamide resin particles 4 are included in thelayer of the resin composition 5. A prepreg 12 shown in (b) of FIG. 1has the same configuration as the prepreg 10 except that it comprises,in place of the surface layer 6 a in the prepreg 10, a surface layer 6 bin which polyamide resin particles 4 are attached to the surface on theopposite side to the reinforcing fiber layer 3 of the layer of the resincomposition 5.

In the prepregs 10 and 12 according to the embodiment, the resincomposition 2 contains (A) a benzoxazine resin, (B) an epoxy resin, and(C) a curing agent having 2 or more phenolic hydroxy groups in amolecule; the surface layers 6 a and 6 b contain (A) a benzoxazineresin, (B) an epoxy resin, (C) a curing agent having 2 or more phenolichydroxy groups in a molecule, and (D) polyamide resin particles havingan average particle size of 5 to 50 μm; and the polyamide resinparticles include a particle made of a copolymer in which caprolactamand laurolactam are copolymerized at a molar ratio of 9:1 to 7:3 andhaving a melting point of 180° C. or more.

As (A) the benzoxazine resin used in the present invention (hereinafter,occasionally referred to as an (A) component), a compound having abenzoxazine ring represented by the following formula (A-1) is given.

In formula (A-1), R⁵ represents a linear alkyl group having 1 to 12carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an arylgroup having 6 to 14 carbon atoms, or an aryl group substituted with alinear alkyl group having 1 to 12 carbon atoms or a halogen. A hydrogenatom may be bonded to the bond.

Examples of the linear alkyl group having 1 to 12 carbon atoms include amethyl group, an ethyl group, a propyl group, an isopropyl group, an-butyl group, an isobutyl group, and a t-butyl group. Examples of thecyclic alkyl group having 3 to 8 carbon atoms include a cyclopentylgroup and a cyclohexyl group. Examples of the aryl group having 6 to 14carbon atoms include a phenyl group, a 1-naphthyl group, a 2-naphthylgroup, a phenanthryl group, and a biphenyl group. Examples of the arylgroup substituted with a linear alkyl group having 1 to 12 carbon atomsor a halogen include an o-tolyl group, a m-tolyl group, a p-tolyl group,a xylyl group, an o-ethylphenyl group, a m-ethylphenyl group, ap-ethylphenyl group, an o-t-butylphenyl group, a m-t-butylphenyl group,a p-t-butylphenyl group, an o-chlorophenyl group, and an o-bromophenylgroup.

As R⁵, of the examples mentioned above, a methyl group, an ethyl group,a propyl group, a phenyl group, and an o-methylphenyl group arepreferable because of providing good handleability.

Furthermore, a compound having benzoxazine rings represented by thefollowing formula (A-2) is given.

In formula (A-2), L represents an alkylene group or an arylene group.

Preferred examples of the benzoxazine resin of the (A) component includethe monomers represented by the following formulae, oligomers in whichseveral molecules of the monomers are polymerized, and reaction productsof at least one of the monomers represented by the following formulaeand a compound having a benzoxazine ring having a structure differentfrom these monomers.

The (A) component forms a skeleton similar to phenol resins by thebenzoxazine ring polymerizing by ring-opening, and is thereforeexcellent in fire retardancy. Furthermore, excellent mechanicalcharacteristics such as a low percentage of water absorption and a highelastic modulus are obtained because of its dense structure.

The (A) component may be used singly or in combinations of two or more.

(B) the epoxy resin (hereinafter, occasionally referred to as a (B)component) used in the present invention controls the viscosity of thecomposition, and is blended as a component that enhances the curabilityof the composition. Preferred examples of the (B) component includeepoxy resins produced using compounds such as amines, phenols,carboxylic acids, and an intramolecular unsaturated carbon or the likeas a precursor.

Examples of the epoxy resins produced using amines as a precursorinclude tetraglycidyldiaminodiphenylmethane, glycidyl compounds ofxylenediamine, triglycidylaminophenol, and glycidylaniline, regioisomersof each thereof and alkyl group- or halogen-substituted productsthereof. Hereinafter, when commercially available products are given asexamples, for liquid products, the complex viscoelastic modulus η* at25° C. obtained with a dynamic viscoelasticity measurement apparatusdescribed later is written as the viscosity.

Examples of the commercially available products oftetraglycidyldiaminodiphenylmethane include “SUMI-EPDXY” (registeredtrademark, the same applies hereinafter) ELM 434 (manufactured bySumitomo Chemical Company, Limited), “Araldite” (registered trademark,the same applies hereinafter) MY 720, “Araldite” MY 721, “Araldite” MY9512, “Araldite” MY 9612, “Araldite” MY 9634, and “Araldite” MY 9663(all manufactured by Huntsman Corporation), and “jER” (registeredtrademark, the same applies hereinafter) 604 (manufactured by MitsubishiChemical Corporation).

Examples of the commercially available products oftriglycidylaminophenol include “jER” 630 (viscosity: 750 mPa·s)(manufactured by Mitsubishi Chemical Corporation), “Araldite” MY 0500(viscosity: 3500 mPa·s) and MY 0510 (viscosity: 600 mPa·s) (bothmanufactured by Huntsman Corporation), and ELM 100 (viscosity: 16000mPa·s) (manufactured by Sumitomo Chemical Company, Limited).

Examples of the commercially available products of glycidylanilinesinclude GAN (viscosity: 120 mPa·s) and GOT (viscosity: 60 mPa·s) (bothmanufactured by Nippon Kayaku Co., Ltd.).

Examples of the glycidyl ether-type epoxy resins produced using a phenolas a precursor include bisphenol A-type epoxy resins, bisphenol F-typeepoxy resins, bisphenol S-type epoxy resins, epoxy resins having abiphenyl skeleton, phenol novolac-type epoxy resins, cresol novolac-typeepoxy resins, resorcinol-type epoxy resins, epoxy resins having anaphthalene skeleton, trisphenylmethane-type epoxy resins,phenolaralkyl-type epoxy resins, dicyclopentadiene-type epoxy resins,diphenylfluorene-type epoxy resins, and various isomers of each thereofand alkyl group- or halogen-substituted products thereof. Also epoxyresins obtained by modifying epoxy resins produced using a phenol as aprecursor with a urethane or an isocyanate are included in this type.

Examples of the commercially available products of liquid bisphenolA-type epoxy resins include “jER” 825 (viscosity: 5000 mPa·s), “jER” 826(viscosity: 8000 mPa·s), “jER” 827 (viscosity: 10000 mPa·s), and “jER”828 (viscosity: 13000 mPa·s) (all manufactured by Mitsubishi ChemicalCorporation), “EPICLON” (registered trademark, the same applieshereinafter) 850 (viscosity: 13000 mPa·s) (manufactured by DICCorporation), “Epotohto” (registered trademark, the same applieshereinafter) YD-128 (viscosity: 13000 mPa·s) (manufactured by NIPPONSTEEL & SUMIKIN CHEMICAL CO., LTD.), and DER-331 (viscosity: 13000mPa·s) and DER-332 (viscosity: 5000 mPa·s) (manufactured by The DowChemical Company). Examples of the commercially available products ofsolid or semisolid bisphenol A-type epoxy resins include “jER” 834,“jER” 1001, “jER” 1002, “jER” 1003, “jER” 1004, “jER” 1004AF, “jER”1007, and “jER” 1009 (all manufactured by Mitsubishi ChemicalCorporation).

Examples of the commercially available products of liquid bisphenolF-type epoxy resins include “jER” 806 (viscosity: 2000 mPa·s), “jER” 807(viscosity: 3500 mPa·s), “jER” 1750 (viscosity: 1300 mPa·s), and “jER”(all manufactured by Mitsubishi Chemical Corporation), “EPICLON” 830(viscosity: 3500 mPa·s) (manufactured by DIC Corporation), and“Epotohto” YD-170 (viscosity: 3500 mPa·s) and “Epotohto” YD-175(viscosity: 3500 mPa·s) (both manufactured by NIPPON STEEL & SUMIKINCHEMICAL CO., LTD.). Examples of the commercially available products ofsolid bisphenol F-type epoxy resins include 4004P, “jER” 4007P, and“jER” 4009P (all manufactured by Mitsubishi Chemical Corporation) and“Epotohto” YDF 2001 and “Epotohto” YDF 2004 (both manufactured by NIPPONSTEEL & SUMIKIN CHEMICAL CO., LTD.).

Examples of the bisphenol S-type epoxy resins include EXA-1515(manufactured by DIC Corporation).

Examples of the commercially available products of epoxy resins having abiphenyl skeleton include “jER” YX4000H, “jER” YX4000, and “jER” YL6616(all manufactured by Mitsubishi Chemical Corporation) and NC-3000(manufactured by Nippon Kayaku Co., Ltd.).

Examples of the commercially available products of phenol novolac-typeepoxy resins include “jER” 152 and “jER” 154 (both manufactured byMitsubishi Chemical Corporation) and “EPICLON” N-740, “EPICLON” N-770,and “EPICLON” N-775 (all manufactured by DIC Corporation).

Examples of the commercially available products of cresol novolac-typeepoxy resins include “EPICLON” N-660, “EPICLON” N-665, “EPICLON” N-670,“EPICLON” N-673, and “EPICLON” N-695 (all manufactured by DICCorporation) and EOCN-1020, EOCN-102S, and EOCN-104S (all manufacturedby Nippon Kayaku Co., Ltd.).

Examples of the commercially available products of resorcinol-type epoxyresins include “Denacol” (registered trademark, the same applieshereinafter) EX-201 (viscosity: 250 mPa·s) (manufactured by NagaseChemteX Corporation).

Examples of the commercially available products of epoxy resins having anaphthalene skeleton include “EPICLON” HP 4032 (manufactured by DICCorporation) and NC-7000 and NC-7300 (both manufactured by Nippon KayakuCo., Ltd.).

Examples of the commercially available products oftrisphenylmethane-type epoxy resins include TMH-574 (manufactured bySumitomo Chemical Company, Limited).

Examples of the commercially available products ofdicyclopentadiene-type epoxy resins include “EPICLON” HP 7200, “EPICLON”HP 7200L, and “EPICLON” HP 7200H (all manufactured by DIC Corporation),“Tactix” (registered trademark) 558 (manufactured by HuntsmanCorporation), and XD-1000-1L and XD-1000-2L (both manufactured by NipponKayaku Co., Ltd.).

Examples of the commercially available products of urethane andisocyanate-modified epoxy resins include AER 4152 having an oxazolidonering (manufactured by Asahi Kasei E-materials Corporation).

Examples of the epoxy resins produced using a carboxylic acid as aprecursor include glycidyl compounds of phthalic acid, glycidylcompounds of hexahydrophthalic acid and dimer acids, and various isomersof each of them.

Examples of the commercially available products of phthalic aciddiglycidyl esters include “EPOMIK” (registered trademark, the sameapplies hereinafter) R508 (viscosity: 4000 mPa·s) (manufactured byMitsui Chemicals, Inc.) and “Denacol” EX-721 (viscosity: 980 mPa·s)(manufactured by Nagase ChemteX Corporation).

Examples of the commercially available products of hexahydrophthalicacid diglycidyl esters include “EPOMIK” R540 (viscosity: 350 mPa·s)(manufactured by Mitsui Chemicals, Inc.) and AK-601 (viscosity: 300mPa·s) (manufactured by Nippon Kayaku Co., Ltd.).

Examples of the commercially available products of dimer acid diglycidylesters include “jER” 871 (viscosity: 650 mPas) (manufactured byMitsubishi Chemical Corporation) and “Epotohto” YD-171 (viscosity: 650mPa·s) (manufactured by NIPPON STEEL & SUMIKIN CHEMICAL CO., LTD.).

Examples of the epoxy resins produced using an intramolecularunsaturated carbon as a precursor include alicyclic epoxy resins.Examples of the alicyclic epoxy resins include(3′,4′-epoxycyclohexane)methyl-3,4-epoxycyclohexanecarboxylate,(3′,4′-epoxycyclohexane)octyl-3,4-epoxycyclohexanecarboxylate, and1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4.1.0]heptane.

Examples of the commercially available products of(3′,4′-epoxycyclohexane)methyl-3,4-epoxycyclohexanecarboxylate include“CELLOXIDE” (registered trademark, the same applies hereinafter) 2021P(viscosity: 250 mPa·s) (manufactured by Daicel Corporation) and CY 179(viscosity: 400 mPa·s) (manufactured by Huntsman Corporation); examplesof the commercially available products of(3′,4′-epoxycyclohexane)octyl-3,4-epoxycyclohexanecarboxylate include“CELLOXIDE” 2081 (viscosity: 100 mPa·s) (manufactured by DaicelCorporation); and examples of the commercially available products of1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4.1.0]heptane include“CELLOXIDE” 3000 (viscosity: 20 mPa·s) (manufactured by DaicelCorporation).

In the embodiment, an epoxy resin that is in a liquid form at 25° C. maybe blended from the viewpoints of tackiness and draping properties. Itis preferable that the viscosity at 25° C. of the epoxy resin that is ina liquid form at 25° C. be as low as possible from the viewpoints oftackiness and draping properties. Specifically, 5 mPa·s or more, whichis the lower limit obtained with commercially available products ofepoxy resins, and 20000 mPa·s or less are preferable, and 5 mPa·s ormore and 15000 mPa·s or less are more preferable. If the viscosity at25° C. is more than 20000 mPa·s, tackiness or draping properties may bereduced.

On the other hand, an epoxy resin that is in a solid form at 25° C. maybe blended from the viewpoint of heat resistance. As the epoxy resinthat is in a solid form at 25° C., epoxy resins having a high aromaticcontent are preferable; and examples include epoxy resins having abiphenyl skeleton, epoxy resins having a naphthalene skeleton, andphenolaralkyl-type epoxy resins.

The (B) component may be used singly or in combinations of two or more.

As (C) the curing agent having 2 or more phenolic hydroxy groups in amolecule (hereinafter, occasionally referred to as a (C) component) usedin the present invention, polyfunctional phenols such as bisphenols aregiven; and examples include bisphenol A, bisphenol F, bisphenol S,thiodiphenol, and bisphenols represented by the following formula (C-1).

In formula (C-1), and R⁴ represent a hydrogen atom or a hydrocarbongroup; when R¹, R², R³, or R⁴ is a hydrocarbon group, they are a linearor branched alkyl group having 1 to 4 carbon atoms, or adjacent R¹ andR² or adjacent R³ and R⁴ bind to form a substituted or unsubstitutedaromatic ring having 6 to 10 carbon atoms or a substituted orunsubstituted alicyclic structure having 6 to 10 carbon atoms; and xrepresents 0 or 1.

Examples of the curing agent represented by the above formula (C-1)include the compounds represented by the following formulae.

In the embodiment, from the viewpoints of the suppression of thereduction in the melting temperature of the polyamide and theimprovement of the heat resistance of the resin cured substance,bisphenol A, bisphenol F, thiobisphenol (hereinafter, occasionallyreferred to as TDP), 9,9-bis(4-hydroxyphenyl)fluorene (hereinafter,occasionally referred to as BPF), and1,1-bis(4-hydroxyphenyl)cyclohexane (hereinafter, occasionally referredto as BPC) are preferable.

The (C) component may be used singly or in combinations of two or more.

In the embodiment, a curing agent other than the (C) component mentionedabove may be used in combination. Examples of the curing agent that canbe used in combination include tertiary aromatic amines typified byN,N-dimethylaniline, tertiary aliphatic amines such as triethylamine,imidazole derivatives, and pyridine derivatives. These may be usedsingly or in combinations of two or more.

(D) the polyamide resin particles having an average particle size of 5to 50 μm (hereinafter, occasionally referred to as a (D) component) usedin the present invention include a particle made of a polyamide 11. Thepolyamide 11 is obtained by polymerizing undecanelactam by ring-opening.The melting point of the polyamide resin particles mentioned above isapproximately 188° C. By using (D) the polyamide resin particles havingthe melting point mentioned above, the polyamide resin particles can bemelted moderately and the CAI and the flexural modulus can be improved,while the polyamide resin particles melting more than necessary andentering the reinforcing fiber layer is suppressed during thepreparation of a fiber-reinforced composite material. The melting pointof (D) the polyamide resin particles is found by increasing thetemperature at a rate of 10° C./minute from 25° C. using a differentialscanning calorimeter (DSC) and measuring the temperature of the top ofthe resulting endothermic peak.

Here, the average particle size of the polyamide resin particles refersto the average value of the measured lengths of the major axes of 100particles selected arbitrarily from particles that are magnified 200 to500 times with a scanning electron microscope (SEM).

As the polyamide resin particles used in the present invention,commercially available products may be used; and examples include“Rilsan PA 11” (registered trademark, manufactured by ARKEMA K.K.).

As the average particle size of the polyamide resin particles mentionedabove, 5 to 50 μm are preferable and 10 to 30 μm are more preferablefrom the viewpoint of controlling the thickness of the surface layer.

In the embodiment, for the amounts of the (A) component and the (B)component contained in the resin composition 2, when it is assumed thatthe total amount of the (A) component and the (B) component is 100 partsby mass, it is preferable that the amount of the (A) component be 65 to80 parts by mass and the amount of the (B) component be 20 to 35 partsby mass, it is more preferable that the amount of the (A) component be65 to 78 parts by mass and the amount of the (B) component be 22 to 35parts by mass, and it is still more preferable that the amount of the(A) component be 70 to 78 parts by mass and the amount of the (B)component be 22 to 30 parts by mass. When the proportion of thecontained (A) component is less than 65 parts by mass, that is, when theproportion of the contained (B) component is more than 35 parts by mass,the elastic modulus and the water resistance of the resultingfiber-reinforced composite tend to be reduced and the glass transitiontemperature of the resin cured substance tends to be reduced.

For the amount of the (C) component contained in the resin composition2, when it is assumed that the total amount of the (A) component and the(B) component is 100 parts by mass, it is preferable to be 5 to 20 partsby mass and it is more preferable to be 7 to 15 parts by mass. If theamount of the contained (C) component is less than 5 parts by mass, ittends to be difficult to sufficiently increase the CAI and the flexuralmodulus in the fiber-reinforced composite material; and in the case ofmore than 20 parts by mass, mechanical properties such as the glasstransition temperature of the cured substance tend to be reduced.

In the embodiment, for the amounts of the (A) component and the (B)component contained in the surface layers 6 a and 6 b, when it isassumed that the total amount of the (A) component and the (B) componentis 100 parts by mass, it is preferable that the amount of the (A)component be 65 to 80 parts by mass and the amount of the (B) componentbe 20 to 35 parts by mass, it is more preferable that the amount of the(A) component be 65 to 78 parts by mass and the amount of the (B)component be 22 to 35 parts by mass, and it is still more preferablethat the amount of the (A) component be 70 to 78 parts by mass and theamount of the (B) component be 22 to 30 parts by mass. If the proportionof the contained (A) component is less than 65 parts by mass, that is,if the proportion of the contained (B) component is more than 35 partsby mass, the elastic modulus and the water resistance of the resultingfiber-reinforced composite tend to be reduced and the glass transitiontemperature of the resin cured substance tends to be reduced.

For the amount of the (C) component contained in the surface layers 6 aand 6 b, when it is assumed that the total amount of the (A) componentand the (B) component is 100 parts by mass, it is preferable to be 5 to20 parts by mass and it is more preferable to be 7 to 15 parts by mass.If the amount of the contained (C) component is less than 5 parts bymass, it tends to be difficult to sufficiently increase the CAI and theflexural modulus in the fiber-reinforced composite material; and in thecase of more than 20 parts by mass, mechanical properties such as theglass transition temperature of the cured substance tend to be reduced.

For the amount of the (D) component contained in the surface layers 6 aand 6 b, when it is assumed that the total amount of the (A) componentand the (B) component is 100 parts by mass, it is preferable to be 15 to45 parts by mass and it is more preferable to be 20 to 40 parts by mass.If the amount of the contained (D) component is less than 15 parts bymass, it tends to be difficult to sufficiently increase the CAI and theflexural modulus in the fiber-reinforced composite material; and in thecase of more than 45 parts by mass, the flexural modulus tends to bereduced.

The surface layers 6 a and 6 b in the prepreg of the embodiment refer tobetween the prepreg surface and the reinforcing fibers of thereinforcing fiber layer, and the amount mentioned above of the (D)component contained in the surface layer can be calculated on the basisof, for example, the amounts of the (A) component, the (B) component,and the (C) component contained detected between the prepreg surface andthe reinforcing fibers of the reinforcing fiber layer.

In the prepreg of the embodiment, another component such as (E) atoughness improver may be blended to the surface layer and thereinforcing fiber layer to the extent that their physical properties arenot impaired. Examples of (E) the toughness improver include phenoxyresins and polyethersulfone.

As still another component, a nanocarbon, a fire retardant, a moldrelease agent, etc. may be blended. Examples of the nanocarbon includecarbon nanotubes, fullerene, and derivatives of each of them. Examplesof the fire retardant include red phosphorus, phosphoric acid esterssuch as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate,cresyl diphenyl phosphate, xylenyl diphenyl phosphate, resorcinolbis(phenyl phosphate), and bisphenol A bis(diphenyl phosphate), andboric acid esters. Examples of the mold release agent include siliconoil, stearic acid esters, and carnauba wax.

As the reinforcing fibers in the present invention, glass fibers, carbonfibers, graphite fibers, aramid fibers, boron fibers, alumina fibers,silicon carbide fibers, and the like may be used. Two or more of thesefibers may be mixed for use. It is preferable to use carbon fibers orgraphite fibers and it is more preferable to use carbon fibers in orderto obtain a molded product that is lighter in weight and higher indurability.

As the carbon fibers used in the present invention, either of PAN-basedcarbon fibers and pitch-based carbon fibers may be used.

In the present invention, any type of carbon fibers or graphite fibersmay be used in accordance with the use. For the tensile elastic modulusin a strand tensile test of the carbon fibers or the graphite fibers, itis preferable to be 150 to 650 GPa, it is more preferable to be 200 to550 GPa, and it is still more preferable to be 230 to 500 GPa because acomposite material that is excellent in impact resistance and has highrigidity and mechanical strength can be obtained. The strand tensiletest refers to a test performed on the basis of JIS R 7601 (1986) aftercarbon fibers or graphite fibers in a bundle form are impregnated withan epoxy resin and curing is performed at a temperature of 130° C. for35 minutes.

The form of the reinforcing fibers in the prepreg and thefiber-reinforced composite material of the embodiment is notparticularly limited; for example, long fibers uniformly extended in onedirection, rattans, textiles, mats, knits, braids, short fibers choppedto a length of less than 10 mm, and the like may be used. Here, the longfiber(s) refers to a single fiber or a fiber bundle substantiallycontinuous for 10 mm or more. The short fiber(s) refers to a fiberbundle cut to a length of less than 10 mm. For uses in which it isrequired for the specific strength and the specific elastic modulus tobe high, an arrangement in which a reinforcing fiber bundle is uniformlyextended in one direction like the prepreg of the embodiment is mostsuitable; but also an arrangement of a cloth (textile) form, which iseasy to handle, can be used.

In the prepreg of the embodiment, for the amount of reinforcing fibersper unit area, it is preferable to be 25 to 3000 g/m² and it is morepreferable to be 70 to 3000 g/m². If the amount of reinforcing fibers isless than 25 g/m², it is necessary to increase the number of stackedsheets in order to obtain a prescribed thickness during molding afiber-reinforced composite material, and operation may be complicated.On the other hand, if the amount of reinforcing fibers is more than 3000g/m², the draping properties of the prepreg tend to be poor. When theprepreg is a flat surface or a simple curved surface, the amount ofreinforcing fibers may be more than 3000 g/m². The percentage ofcontained fibers in the prepreg is preferably 30 to 90 mass %, morepreferably 35 to 85 mass %, and still more preferably 40 to 80 mass %.If the content percentage is less than 30 mass %, the amount of theresin is too large; and the advantage of a fiber-reinforced compositematerial excellent in specific strength and specific elastic modulus maynot be obtained, or during the molding of a fiber-reinforced compositematerial, the amount of heat generated during curing may be too large.If the content percentage is more than 90 mass %, an impregnation defectof the resin occurs and the resulting composite material tends toinclude a large amount of voids.

Next, production methods for prepregs according to the present inventionare described. FIG. 2 and FIG. 3 are schematic cross-sectional views fordescribing production methods for prepregs according to the presentinvention. The method shown in FIG. 2 is an embodiment of the productionmethod for the prepreg 10 according to the embodiment described above.In this method, a reinforcing fiber bundle 7 in which reinforcing fibers1 are uniformly extended in one direction is prepared (a), thereinforcing fiber bundle 7 is impregnated with a first resin composition2 containing the (A) to (C) components mentioned above to form thereinforcing fiber layer 3 (b), and both surfaces of the reinforcingfiber layer 3 are impregnated with a second resin composition containingthe (A) to (C) components and the (D) component mentioned above to formthe surface layers 6 a and thus the prepreg 10 is obtained (c).

In the method shown in FIG. 3, a reinforcing fiber bundle 7 in whichreinforcing fibers 1 are uniformly extended in one direction is prepared(a), and both surfaces of the reinforcing fiber bundle 7 are impregnatedwith a resin composition containing the (A) to (D) components mentionedabove once to form the surface layers 6 a made of the resin composition2 containing the (D) component 4 with which fibers have not beenimpregnated and the (A) to (C) components and thus a prepreg 11 isobtained (c).

The prepreg 12 of FIG. 1(b) can be produced by, for example,impregnating a reinforcing fiber bundle with a resin compositioncontaining the (A) to (C) components and then sprinkling the (D)component over the surfaces of the reinforcing fiber bundle impregnatedwith the resin composition.

Each resin composition with which the reinforcing fiber bundle isimpregnated can be prepared by kneading the (A) to (C) componentsmentioned above and, as necessary, other components, or the (A) to (D)components mentioned above and, as necessary, other components.

The method for kneading a resin composition is not particularly limited;for example, a kneader, a planetary mixer, a biaxial extruder, etc. areused. It is preferable that, from the viewpoint of the dispersibility ofthe particle components of the (D) component etc., the particles bediffused into liquid resin components beforehand with a homomixer, threerolls, a ball mill, a bead mill, ultrasonic waves, and the like.Furthermore, during mixing with a matrix resin, during preliminarydiffusion of particles, or in other cases, it is possible to performheating or cooling, or pressurization or depressurization, as necessary.After kneading, immediate storage in a refrigerator or a freezer ispreferable from the viewpoint of storage stability.

As the viscosity of the resin composition, 10 to 20000 Pa·s at 50° C.are preferable from the viewpoint of the production of a precursor film.10 to 10000 Pa·s are more preferable, and 50 to 6000 Pa·s are mostpreferable. In the case of less than 10 Pas, the tackiness of the resincomposition may be increased, and coating may be difficult. In the caseof more than 20000 Pa·s, semisolidification occurs and coating isdifficult.

Examples of the method for impregnating fibers with a resin compositioninclude the wet method in which a resin composition is dissolved in asolvent such as methyl ethyl ketone or methanol to be reduced inviscosity and impregnation therewith is performed and the hot meltmethod (dry method) in which the viscosity is reduced by heating andimpregnation is performed.

The wet method is a method in which reinforcing fibers are immersed in asolution of a resin composition and then pulled up and the solvent isvaporized using an oven or the like. The hot melt method is a method inwhich reinforcing fibers are directly impregnated with a resincomposition that has been reduced in viscosity by heating or a method inwhich a resin composition is once applied onto a mold release papersheet or the like in a coating manner to fabricate a film, subsequentlythe film is superposed from both sides or one side of reinforcingfibers, and heating and pressurization are performed to impregnate thereinforcing fibers with the resin. The hot melt method is preferablebecause there is substantially no solvent remaining in the prepreg.

The prepreg according to the present invention can be made into afiber-reinforced composite material by a method in which, afterstacking, the resin is cured by heating while pressure is applied to thestacked matter or other methods. Here, examples of the method forapplying heat and pressure include the press molding method, theautoclave molding method, the bagging molding method, the wrapping tapemethod, and the internal pressure molding method. The wrapping tapemethod is a method in which a prepreg is wound around a cored bar suchas a mandrel and a tubular body made of a fiber-reinforced compositematerial is molded, and is a method suitable in fabricating stick-likebodies such as golf shafts and fishing rods. More specifically, it is amethod in which a prepreg is wound around a mandrel, a wrapping tapeformed of a thermoplastic film is wound on the outside of the prepreg inorder to fix and apply pressure to the prepreg, the resin is cured byheating in an oven, and then the cored bar is taken out to obtain atubular body.

The internal pressure molding method is a method in which a preform inwhich a prepreg is wound around an internal pressure applier such as atube made of a thermoplastic resin is set in a mold, and subsequently ahigh pressure gas is introduced into the internal pressure applier toapply pressure and at the same time the mold is heated to performmolding. This method is preferably used in molding complicated shapedobjects such as golf shafts, bats, and rackets for tennis, badminton,etc.

A composition containing resin particles that contains the (A) to (D)components mentioned above and, as necessary, other components can besuitably used for the preparation of the prepreg described above. Acomposition containing resin particles in which the amount of thecontained (D) component is 15 to 45 parts by mass and preferably 20 to40 parts by mass when it is assumed that the total amount of the (A)component and the (B) component is 100 parts by mass can be suitablyused as the material for forming the surface layer of the prepreg. Forthe composition containing resin particles, it is preferable that theglass transition temperature of its cured substance obtained byincreasing the temperature at 2° C./min and then performing curing underthe conditions of 180° C. and 2 hours be 190° C. or more.

FIG. 4 is a schematic cross-sectional view for describing afiber-reinforced composite material according to the present invention.A fiber-reinforced composite material 100 shown in FIG. 4 comprisesreinforcing fibers 1, a resin cured substance 8, and polyamide resinparticles 4. The fiber-reinforced composite material 100 can be obtainedby stacking any one of the prepregs 10, 11, and 12 plurally andperforming heating under increased pressure.

In the fiber-reinforced composite material, for the volume proportion ofC₁ in the total amount of the amount C₁ of the polyamide resin containedin the resin cured substance between reinforcing fiber layers and theamount C₂ of the polyamide resin contained in the reinforcing fiberlayers, {C₁/(C₁+C₂)}×100, it is preferable to be 70 volume % or more andit is more preferable to be 80 volume % or more.

The amount of the contained polyamide resin is found by analyzing, bymicroscopic observation, a cross section of the fiber-reinforcedcomposite material taken along a plane orthogonal to the direction inwhich an arbitrary reinforcing fiber in the fiber-reinforced compositematerial extends and performing image analysis to observe thedistribution of the polyamide resin.

The fiber-reinforced composite material according to the presentinvention can be obtained also by directly impregnating a reinforcingfiber matrix with a resin composition and performing curing. Forexample, the production can be performed by a method in which areinforcing fiber matrix is placed in a mold and then a resincomposition containing the (A) to (D) components mentioned above ispoured in followed by impregnation and curing, or a method in which areinforcing fiber matrix and a film formed of a resin compositioncontaining the (A) to (D) components mentioned above are stacked and thestacked body is heated and pressurized. The film mentioned above can beobtained by applying a prescribed amount of a resin composition with auniform thickness onto a mold release paper sheet or a mold release filmbeforehand. Examples of the reinforcing fiber matrix include long fibersuniformly extended in one direction, bidirectional textiles, unwovenfabrics, mats, knits, and braids. The stacking herein includes not onlythe case where fiber matrices are simply superposed but also the casewhere preforming is performed by attachment to various molds or corematerials. As the core materials, foam cores, honeycomb cores, and thelike are preferably used. As the foam cores, urethanes and polyimidesare preferably used. As the honeycomb cores, aluminum cores, glasscores, aramid cores, and the like are preferably used.

In the fiber-reinforced composite material according to the presentinvention, for the compressive strength after impact (CAI) measured inaccordance with SACMA SRM 2R-94, it is preferable to be 210 MPa or moreand it is more preferable to be 220 MPa or more.

In the fiber-reinforced composite material according to the presentinvention, for the glass transition temperature of the resin curedsubstance, it is preferable to be 180° C. or more and it is morepreferable to be 190° C. or more.

The fiber-reinforced composite material according to the presentinvention having the physical properties mentioned above is suitablyused for railroad vehicles, aircraft, building members, and othergeneral industrial uses.

Examples

The present invention will now be specifically described using Examples,but the present invention is not limited to them. The measurements ofvarious physical properties are based on the following methods. Theresults are shown in Table 1.

Examples 1 to 3 and Comparative Examples 1 to 2

For Examples and Comparative Examples, the source materials were mixedwith heating at the ratios shown in Table 1, and a first resincomposition containing no particles (the “first” composition in Table)and a second resin composition containing particles (the “second”composition in Table) were obtained. The source materials used here areas follows.

The (A) component: a benzoxazine resin

F-a (a bisphenol F-aniline type, manufactured by SHIKOKU CHEMICALSCORPORATION)P-a (a phenol-aniline type, manufactured by SHIKOKU CHEMICALSCORPORATION)The (B) component: an epoxy resin“CELLOXIDE” (registered trademark) 2021P (manufactured by DaicelCorporation)The (C) component: a curing agentBPF (9,9-bis(4-hydroxyphenyl)fluorene, manufactured by Osaka GasChemicals Co., Ltd.)BPC (1,1-bis(4-hydroxyphenyl)cyclohexane, manufactured by Sigma-AldrichCo. LLC.)TDP (bis(4-hydroxyphenyl) sulfide, manufactured by Tokyo ChemicalIndustry Co., Ltd.)The (D) component: polyamide resin particlesPA 11 (polyamide 11, average particle size: 25 μm, manufactured byARKEMA K.K.)The (D′) component: polyamide resin particlesPA 6 (polyamide 6, average particle size: 20 μm, manufactured byDaicel-Evonik Ltd.)PA 12 (polyamide 12, average particle size: 20 μm, manufactured byDaicel-Evonik Ltd.)The (E) component: a toughness improverA phenoxy resin (YP-70, manufactured by NIPPON STEEL & SUMIKIN CHEMICALCO., LTD.)

<Production of a Prepreg>

The first and second resin compositions obtained were each applied ontoa mold release paper sheet at 70 to 100° C. to obtain a first resin filmwith 18 g/m² and a second resin film with 25 g/m². The first resin filmobtained was supplied from the upper and lower sides of carbon fibersuniformly extended in one direction and the space between fibers wasimpregnated therewith to form a carbon fiber layer. Subsequently, thesecond resin film was laminated from the upper and lower sides of thecarbon fiber layer to form surface layers; thus, a prepreg was prepared.The amount of carbon fibers per unit area of the prepreg was 150 g/m²,and the total amount of the resin composition in the carbon fiber layerand the surface layers (amount of matrix resin) was 86 g/m².

<Measurement of the Melting Point of the Polyamide Resin Particles>

The polyamide resin particles that are the (D) component and the (D′)component mentioned above were increased in temperature at a rate of 10°C./minute from 25° C. using a differential scanning calorimeter (DSC),and the top of the resulting endothermic peak was taken as the meltingpoint of the polyamide resin particles. The results are shown in Table2. A DSC chart of PA 11 is shown in FIG. 5.

<Measurement of the Melting Temperature of the Polyamide Resin Particlesin the Second Resin Composition>

The second resin composition obtained was increased in temperature at arate of 10° C./minute from 25° C. using a differential scanningcalorimeter (DSC), and the top of the resulting endothermic peak wastaken as the melting temperature of the polyamide resin particles in thesecond resin composition. The results are shown in Table 1. A DSC chartof the second resin composition of Example 3 is shown in FIG. 6.

<Measurement of the Glass Transition Temperature>

The second resin composition obtained was cured for 2 hours in an ovenof 180° C. to obtain a resin cured substance. For the cured substanceobtained, the middle point temperature found on the basis of JIS K 7121(1987) using a differential scanning calorimeter (DSC) was measured asthe glass transition temperature. The results are shown in Table 1.

<Measurement of the Flexural Modulus>

The second resin composition obtained was cured for 2 hours at atemperature of 180° C. to obtain a resin cured substance. For the resincured substance, the flexural modulus was measured in accordance withJIS J. 7171. The results are shown in Table 1.

<Measurement of the CAI>

Prepregs obtained were stacked 32 plies pseudo-isotropically with aconfiguration of [+45°/0°/−45°/90° ]_(4s), were increased in temperaturein an autoclave at 2° C./minute from room temperature to 180° C. at apressure of 0.6 MPa, and were then cured by heating for 2 hours at thesame temperature; thus, a CFRP was obtained. From the CFRP, inaccordance with SACMA SRM 2R-94, a sample of 150 mm long×100 mm broadwas cut out, and a falling weight impact of 6.7 J/mm was applied to acentral portion of the sample; thus, the compressive strength afterimpact was found. The results are shown in Table 1.

<The Abundance Ratio (Volume %) of the Polyamide Resin Between CarbonFiber Layers>

A cross section of the fiber-reinforced composite material taken along aplane orthogonal to the direction in which an arbitrary carbon fiber inthe fiber-reinforced composite material extends was analyzed bymicroscopic observation (500 times), and image analysis was performedfor a range of 500 μm×100 μm to observe the distribution of polyamideparticles; thereby, the amount C₁ of the polyamide resin contained inone piece of the resin cured substance between carbon fiber layers andthe amount C₂ of the polyamide resin contained in one carbon fiber layerwere calculated. This measurement was performed on arbitrary 5 placesthat are combinations of different carbon fiber layers and differentpieces of the resin cured substance, and the average value of the 5places of C₁ and C₂ was used to find the volume proportion of C₁,{C₁/(C₁+C₂)}×100, per prepreg. The results are shown in Table 1.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 1Example 2 Component Source material First Second First Second FirstSecond First Second First Second (A) F-a 70 70 70 70 70 70 70 70 70 70P-a 5 5 5 5 5 5 5 5 5 5 (B) CELLOXIDE 2021P 25 25 25 25 25 25 25 25 2525 (E) Phenoxy resin YP-70 5 5 5 5 5 5 5 5 5 5 (C) BPF 10 10 — — — — — —— — BPC — — 10 10 — — — — — — TDP — — — — 10 10 10 10 10 10 (D) PA11 (25μm) — 29 — 29 — 29 — — — — (D′) PA6 (20 μm) — — — — — — — — — 29 PA12(20 μm) — — — — — — — 29 — — Melting temperature of polyamide — 170 —167 — 163 — 156 — 200 resin particles (° C.) (in second resincomposition) Glass transition temperature (° C.) — 198 — 194 — 194 — 194— 194 Flexural modulus (MPa) — 4120 — 4060 — 4000 — 3920 — 4400 CAI(MPa) 275 263 249 200 180 Abundance ratio (volume %) of 88 85 80 30 90polyamide resin between carbon fiber layers

TABLE 2 Polyamide resin particles Melting point (° C.) PA11 188 PA6 225PA12 184

As shown in Table 1, it has been found that, in Examples 1 to 3 in whichthe specific (D) polyamide resin particles were used, an excellent CAIand flexural modulus can be achieved at a high level at the same time,and also the glass transition temperature of the resin material can bekept high.

INDUSTRIAL APPLICABILITY

According to the present invention, a prepreg that makes it possible toobtain a fiber-reinforced composite material that, while using abenzoxazine resin having excellent moisture resistance and heatresistance, can achieve an excellent CAI and flexural modulus at highlevel at the same time and can also keep the glass transitiontemperature of the resin material high, a resin composition containingparticles for obtaining the prepreg, and a fiber-reinforced compositematerial can be provided.

The fiber-reinforced composite material of the present invention can besuitably used for aircraft uses, vessel uses, automobile uses, sportsuses, and other general industrial uses, and is useful particularly foraircraft uses.

REFERENCE SIGNS LIST

1 . . . reinforcing fibers, 2 . . . resin composition, 3 . . .reinforcing fiber layer, 4 . . . polyamide resin particles, 5 . . .resin composition, 6 a, 6 b . . . surface layer, 7 . . . reinforcingfiber bundle, 8 . . . resin cured substance, 10, 11 . . . prepreg, 100 .. . fiber-reinforced composite material.

1. A prepreg comprising: a reinforcing fiber layer including reinforcingfibers and a resin composition with which the space between fibers ofthe reinforcing fibers is impregnated and which contains (A) abenzoxazine resin, (B) an epoxy resin, and (C) a curing agent having 2or more phenolic hydroxy groups in a molecule; and a surface layerprovided on at least one surface of the reinforcing fiber layer andcontaining (A) a benzoxazine resin, (B) an epoxy resin, (C) a curingagent having 2 or more phenolic hydroxy groups in a molecule, and (D)polyamide resin particles having an average particle size of 5 to 50 μm,wherein the polyamide resin particles include a particle made of apolyamide
 11. 2. The prepreg according to claim 1, wherein the surfacelayer contains 65 to 80 parts by mass of the (A) component, 20 to 35parts by mass of the (B) component, 5 to 20 parts by mass of the (C)component, and 15 to 45 parts by mass of the (D) component when it isassumed that the total amount of the (A) component and the (B) componentis 100 parts by mass.
 3. A fiber-reinforced composite material obtainedby stacking the prepreg according to claim 1 plurally and performingheating under increased pressure.
 4. A resin composition containingparticles comprising: (A) a benzoxazine resin; (B) an epoxy resin; (C) acuring agent having 2 or more phenolic hydroxy groups in a molecule; and(D) polyamide resin particles having an average particle size of 5 to 50μm, wherein the polyamide resin particles include a particle made of apolyamide
 11. 5. A fiber-reinforced composite material obtained bystacking the prepreg according to claim 2 plurally and performingheating under increased pressure.